So-called mobile spas are a dime a dozen: Providers will bring massage tables, manicure tools and aromatherapy oils to a home or office, then set up shop and provide their services in your den or your company’s conference room. Renewal Retreat Onsite is a little different in that the employer or party host booking it doesn’t need a place — well, maybe an oversized parking spot, but that’s it. The “retreat” is a customized RV that travels throughout San Francisco and Silicon Valley, delivering facials, mani-pedis and other treatments right inside the vehicle.